Question: Solve for $x$ and $y$ using substitution. ${3x+y = 9}$ ${y = -4x+11}$
Since $y$ has already been solved for, substitute $-4x+11$ for $y$ in the first equation. ${3x + }{(-4x+11)}{= 9}$ Simplify and solve for $x$ $3x-4x + 11 = 9$ $-x+11 = 9$ $-x+11{-11} = 9{-11}$ $-x = -2$ $\dfrac{-x}{{-1}} = \dfrac{-2}{{-1}}$ ${x = 2}$ Now that you know ${x = 2}$ , plug it back into $\thinspace {y = -4x+11}\thinspace$ to find $y$ ${y = -4}{(2)}{ + 11}$ $y = -8 + 11$ $y = 3$ You can also plug ${x = 2}$ into $\thinspace {3x+y = 9}\thinspace$ and get the same answer for $y$ : ${3}{(2)}{ + y = 9}$ ${y = 3}$